J.M.C. Bueno

Co/SiO2 catalysts for selective hydrogenation of crotonaldehyde II: influence of the Co surface structure on selectivity

Abstract The effect of interaction of silica-supported CoO x on catalytic properties of Co/SiO 2 catalysts was investigated. The CoO x precursors supported on silica were obtained by impregnation of the support with cobalt nitrate solution. Cobalt precursors, with different interactions with support, were obtained by changes of impregnation solvent, drying time and temperature; and calcination temperature. The Co surface structure of the catalysts was characterized by diffuse reflectance FTIR spectroscopy (DRIFTS) of adsorbed CO and temperature-programmed desorption of hydrogen (TPD-H 2 ). The TPD-H 2 and DRIFT of CO spectra indicate the presence of at least four different Co surface sites, labeled α , β , γ , and σ . The relative amount of these species varied depending on the degree of CoO x interaction with SiO 2 in precursors. For crotonaldehyde (CROALD) hydrogenation in gas phase, selectivity to crotyl alcohol and butanol depended strongly on the β /( γ + σ ) ratio. Interestingly, selectivity to butyraldehyde does not depend on β , γ , or σ sites present.

CO2 reforming of CH4 over Rh-containing catalysts

Abstract Two series Rh catalysts were prepared depending on the kind of the support: (i) Rh supported on zeolite and (ii) on oxide carriers. Rh/NaY zeolite catalysts were prepared by ion-exchange from an aqueous solution of [Rh(NH 3 ) 5 ]Cl 3 . Rh catalysts supported on γ-Al 2 O 3 , Nb 2 O 5 and TiO 2 were prepared by incipient wetness impregnation method of the carrier with an aqueous solution of RhCl 3 ·2H 2 O. The catalysts were characterized by X-ray diffraction (XRD) spectroscopy, nuclear magnetic resonance (NMR), temperature-programmed desorption of hydrogen (TPD-H 2 ). Test reaction for Rh catalysts was CO 2 reforming of methane at different reaction temperatures. TPD data showed that the dispersion of metal particles depends on the pretreatment activation procedure; highest dispersion was observed for samples previously calcined and then activated in H 2 . Catalysts activated directly in H 2 , steam or submitted directly to the reaction conditions showed large metal particles. The effect of the protons on the destabilization of the zeolite framework during reaction was revealed by the higher Si/Al ratios, due to a dealumination of the zeolite. Neutralization of protons with solution of NaOH leaded to a stabilization of the dispersion and zeolite structure. Correlation between the dispersion and specific activity in CO 2 reforming was found for zeolite-supported Rh catalysts. When the activities are compared by turnover frequencies, oxide-supported Rh catalysts are significantly more active compared to zeolite-supported ones due to a higher degree of participation of the reverse water–gas shift reaction (WGSR). The difference in activity and thermal stability was related to the nature of the support.

CO2 reforming of methane over zeolite-Y supported ruthenium catalysts

Ru/HY and Ru/NaY catalysts were prepared by ion-exchange from an aqueous solution of [Ru(NH3)6]Cl3. The catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR). The results showed that Si/Al ratio of the zeolite framework after use depends on the catalyst preparation procedure. Upon activation in He, Si/Al ratio in Ru/NaY is similar to that of initial zeolite NaY. After exposure to reaction conditions, NMR data show dealumination, whose extent increases with Ru loading. Samples activated in He followed by ion exchange with NaNO3 (neutralization) and reactivated in CH4/CO2/N2 undergo only slight dealumination. The results suggest that during reaction the charge compensating protons, generated during Ru reduction, cause dealumination, accompanied by local destruction of the zeolite structure. The structure of zeolite and Ru dispersion was therefore, stabilized and the catalyst specific activity increased by neutralizing the protons prior to use in CO 2 reforming. ©2000 Elsevier Science B.V. All rights reserved.

Selective oxidation of methane to methanol and formaldehyde over V2O5/SiO2 catalysts. Role of NO in the gas phase

The role of nitric oxide incorporation into the reaction feed for the partial oxidation of methane to C2-hydrocarbons and C2-oxygenates is evaluated. The addition of NO increases the conversion of methane under all the experimental conditions studied and has a strong effect on the product distribution. At low NO concentration the catalysts yield mainly C2Hn hydrocarbons, but at higher NO concentrations, carbon oxides dominate. Amongst the C1-oxygenates produced, methanol is the major compound observed and its proportion increases with increasing NO concentration. The highest C1-oxygenates yield was 7% at atmospheric pressure.

Catalytic transformations of ethanol for biorefineries.

Brazil and the USA are the major bioethanol producers in the world, and the main application of this alcohol is as fuel. Since Brazilian ethanol is the cheapest in the world, there is a crescent interest in its use as a building block for biorefineries. Bioethanol can be used for the direct production of drop-in chemicals, such as ethylene, propylene, 1,3-butadiene and larger hydrocarbons, as well as for the production of oxygenated molecules, such as 1-butanol, ethyl acetate, acetaldehyde, and acetic acid. In this critical review, the development of heterogeneous catalysts for the conversion of ethanol into these commodity chemicals will be discussed.

CO2 reforming of CH4 over Ru/zeolite catalysts modified with Ti

Abstract Ru/NaY and Ru/USY catalysts were prepared by ion exchange from an aqueous solution of [Ru(NH 3 ) 6 ]Cl 3 . The effect of titanium on the structure of Ru/zeolite introduced by ion exchange or impregnation method from aqueous solution of (NH 4 ) 2 TiO(C 2 O 4 ) 2 ·H 2 O was investigated. The samples were characterized by different techniques, using X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), temperature-programmed desorption of hydrogen (TPD-H 2 ), Fourier transform infrared spectroscopy (FTIR) of CO adsorption and transmission electron microscopy (TEM). Introduction of titanium into Ru/NaY zeolite by ion exchange caused a significant structural collapse of the zeolite framework. Contrary to that, TEM data showed that Ti incorporated into Ru/USY by ion exchange was well distributed within the zeolite cavities. The crystallinity of the USY zeolite decreased significantly after introduction of Ti by impregnation method and a separate phase of titania was formed. The effect of Ti content on the catalytic behavior of zeolite-supported Ru catalysts in the reaction of CO 2 reforming of CH 4 was elucidated. The higher specific activity of Ti-containing catalysts related to CO formation was caused by the both factors, the acceleration of CH x O decomposition (precursor for CO formation) on metal-support interface and participation of the reverse of water gas shift reaction.

Supported VPO catalysts for selective oxidation of butane III: Effect of preparation procedure and SiO2 support

Abstract The effects of the nature of silica support and removal of soluble vanadium species by ethanol on the catalytic properties of silica-supported VPO catalysts were investigated. Ethanol preferentially removes V +5 species. For a silica-supported sample of P / V ratio much lower than two, ethanol treatment resulted in a sample of higher P / V ratio and higher selectivity for maleic anhydride in butane oxidation. The crystalline VPO phases formed differed on a hydrophobic vs. hydrophilic silica. (VO) 2 P 2 O 7 could be formed more easily on the former support. Interestingly, for all silica-supported catalysts, the maleic anhydride selectivity depended much more strongly on the P / V ratio than on the method of preparation, the nature of the silica, or the crystalline VPO phase present.

An infrared study of CO adsorption on silica-supported Ru-Sn catalysts.

CO adsorption on Ru-Sn/SiO(2) catalysts of various Sn/(Ru+Sn) ratios was examined by Diffuse Reflectance Infrared Fourier-Transform Spectroscopy (DRIFTS). The catalysts were prepared by the incipient wetness impregnation method. Catalysts were activated by H(2) reduction at 773 K. CO adsorbed on the catalysts shows spectra whose band frequencies are divided into three groups: (i) High Frequency Region (HFR), containing a band at 2065 cm(-1), (ii) Low Frequency Region 1 (LFR(1)), containing bands at 2040-2015 cm(-1), (iii) Low Frequency Region 2 (LFR(2)), containing bands at 1990 and 1945 cm(-1). The types of adsorbed CO species formed strongly depend on the ratio Sn/(Ru+Sn) in the catalyst, CO pressure and temperature of adsorption. Adsorption of CO on Ru sites in the Ru/SiO(2) catalyst results in LFR(1) bands at 2040-2015 cm(-1), which are independent of the CO pressure but the adsorption complexes are easily destroyed by raising the temperature. The addition of Sn to the catalyst creates new sites for CO adsorption. After adsorption at 298 K, the HFR band at 2065 cm(-1) and LFR(2) bands at 1990-1950 cm(-1) are observed. The relative intensities of these bands increase with increasing Sn-content in the samples. The LFR bands are thermally stable while the HFR band is not. The formation of the corresponding species is favored by increasing the CO pressure. Adsorbed CO species giving LFR(1) bands are assigned to linearly-adsorbed CO on the Ru(0) and/or on the Ru-Sn alloy sites. Adsorbed CO species giving HFR bands are assigned to CO adsorption on Ru(delta+)-O-Sn sites. After low temperature CO adsorption on samples with high Sn-content, only species that show bands at 1990 and 1945 cm(-1) in LFR(2) are observed.

Insight into Copper‐Based Catalysts: Microwave‐Assisted Morphosynthesis, In Situ Reduction Studies, and Dehydrogenation of Ethanol

Herein, we report results of three distinct controlled CuO morphologies, urchin-like (CuO-UC), fiber-like (CuO-FB) and nanorods (CuO-NR), prepared by MWA method. These well-designed structures were then dispersed in silica (SiO2) and reduced in a H2 flow that produced the following catalysts: CuO1� xUC, CuO1� xFB, and CuO1� xNR (x = 0, 1, and/or 2); their subsequent activity for the dehydrogenation of ethanol is also discussed herein. The activity and selectivity of these catalysts depend on the physical and chemical structure of the active components, which are largely influenced by the catalyst preparation method. [13] In particular, the use of small-sized CuO crystals produced a highly active and selective catalyst for the dehydrogenation of ethanol into acetaldehydes with high turnover frequencies (TOF). The structural characterization of catalysts was carried out by using several ex situ techniques; highresolution field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), conventional temperature-programmed reduction under H2 (TPR-H2), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) method for surface area determination, and in situ time-resolved X-ray absorption near-edge structure (XANES) spectroscopy at the Cu K-edge during TPR under H2 experiments (XANES–TPR-H2). Complete experimental details are provided in the Supporting Information. In addition, the Cu metal surface after the reduction treatment of the samples was subjected to TPR measurements with N2O oxidation. [14] FESEM images of CuO assemblies with different morphologies obtained by efficient MWA synthesis are shown in Figure 1 . Our results show that both the solvent and the base influence the final shape of crystals. By using copper(II) chloride dihydrate in deionized water and ammonium hydroxide as the base, CuO-UC structures were obtained with an average size of 3 mm in diameter and nanostructured spines (10 nm of

Influence of the surface structure of Co on the selective hydrogenation of crotonaldehyde

Two series of Co/SiO 2 catalysts prepared by impregnation, using water and ethanol as solvents, were tested in hydrogenation of crotonaldehyde in gas phase. Four types of chemisorbed hydrogen species on the cobalt surface were identified by TPD and labeled α, β, γ and σ. It was established that selectivity towards crotyl alcohol depends on preferential generation of “β” sites as opposed to “γ” and “σ” sites on the metal cobalt surface. Increase of “γ” and “σ” sites leads to a butanol selectivity increase. The “β” site generation directly dependens on Co loading and CoO x -SiO 2 interaction in the precursor. Silica and CoO x interaction depends strongly on the solvent utilized for impregnation and on drying and calcination temperature.